FIG. 1 is a block diagram of a network structure of UMTS (universal mobile telecommunications system).
Referring to FIG. 1, a universal mobile telecommunications system (hereinafter abbreviated UMTS) mainly includes a user equipment (hereinafter abbreviated UE), a UMTS terrestrial radio access network (hereinafter abbreviated UTRAN), and a core network (hereinafter abbreviated CN).
The UTRAN includes at least one radio network sub-system (hereinafter abbreviated RNS). And, the RNS includes one radio network controller (hereinafter abbreviated RNC) and at least one base station (hereinafter called Node B) managed by the RNC. And, at least one or more cells exist in one Node B.
An interface between RNCs is called Iur interface and another interface between RNC and Node B is called Iub interface. And, another interface between RNC and CN is called Iu interface.
Meanwhile, RNC responsible for a major function of controlling one user equipment (UE) is called SRNC (serving RNC) of the corresponding UE. And, another RNC, which is not responsible for the major function of controlling the corresponding UE but provides radio resources for the UE, is called DRNC (drift RNC) of the corresponding UE.
A protocol responsible for control message exchange between SRNC and DRNC is called RNSAP (radio network subsystem application part) and a protocol responsible for control message exchange between RNC and Node B is called NBAP (Node B application part).
FIG. 2 is an architectural diagram of a radio interface protocol between UE (user equipment) and UTRAN (UMTS terrestrial radio access network) based on the 3GPP radio access network standard.
Referring to FIG. 2, a radio interface protocol vertically includes a physical layer, a data link layer, and a network layer and horizontally includes a user plane for data information transfer and a control plane for signaling transfer.
The protocol layers in FIG. 2 can be divided into L1 (first layer), L2 (second layer), and L3 (third layer) based on three lower layers of the open system interconnection (OSI) standard model widely known in the communications systems.
The respective layers in FIG. 2 are explained as follows.
First of all, the physical layer (hereinafter named PHY) as the first layer offers an information transfer service to an upper layer using a physical channel. The physical layer PHY is connected to a medium access control (hereinafter abbreviated MAC) layer above the physical layer PHY via a transport channel. And, data are transferred between the medium access control layer MAC and the physical layer PHY via the transport channel. Moreover, data are transferred between different physical layers, and more particularly, between one physical layer of a transmitting side and the other physical layer of a receiving side via the physical channel.
The medium access control (hereinafter abbreviated MAC) layer of the second layer offers a service to a radio link control layer above the MAC layer via a logical channel.
The radio link control (hereinafter abbreviated RLC) layer of the second layer supports reliable data transfer and is operative in segmentation and concatenation of RLC service data units sent down from an upper layer. Hereinafter, the service data unit will be abbreviated SDU.
A radio resource control (hereinafter abbreviated ‘RRC’) layer located on a lowest part of the third layer is defined in the control plane only and is associated with configuration, reconfiguration and release of radio bearers to be in charge of controlling the logical, transport and physical channels (hereinafter, the radio bearer will be abbreviated RB).
In this case, the RB means a service offered by the second layer for the data transfer between the UE and the UTRAN. And, the configuration of RB means a process of regulating characteristics of protocol layers and channels necessary for offering a specific service and a process of setting their specific parameters and operational methods, respectively.
If an RRC layer of a specific UE and an RRC layer of UTRAN are connected together to exchange an RRC message, the corresponding UE is in a connected state. If not, the corresponding UE is in an idle state.
A generic access network (hereinafter abbreviated GAN) is explained as follows.
First of all, GAN can be called UMA (unlicensed mobile access) and is a system that supports seamless roaming between a UTRAN and a wireless LAN. And, GAN UE which supports the UTRAN and the wireless LAN by supporting the GAN is able to switch to the wireless LAN without access interruption in moving away into an area having a weak UTRAN signal and a strong wireless LAN signal. For this, a network supports GANC (GAN controller).
However, in the related art, a clear procedure for executing handover between heterogeneous networks has not been defined. And, the DRNC of the related art is unable to know whether a specific UE is able to support the GAN. So, the UTRAN is unable to know whether to inform the corresponding UE of information for GAN cell near a cell controlled by the DRNC. If the DRNC is unable to know this fact, the DRNC should give the information for the GAN cell to all UEs. Hence, signaling overhead is generated in the RRC interface and network interface.